The present disclosure relates, in various embodiments, to thin-film transistors (TFTs) and/or other electronic devices comprising a semiconducting layer and a gate dielectric layer. The gate dielectric layer comprises a poly(4-vinylphenol-co-acrylonitrile) (PVPA) based polymer. The resulting dielectric layer has a high dielectric constant and can be crosslinked. Certain gate dielectric layer thicknesses can therefore still prevent current leakage while having a large capacitance, enabling low operating voltages.
TFTs are generally composed of, on a substrate, an electrically conductive gate electrode, source and drain electrodes, an electrically insulating gate dielectric layer which separate the gate electrode from the source and drain electrodes, and a semiconducting layer which is in contact with the gate dielectric layer and bridges the source and drain electrodes. Their performance can be determined by the field effect mobility and the current on/off ratio. High mobility and high on/off ratio are desired.
There is interest in organic thin film transistors (OTFTs) for applications such as radio frequency identification (RFID) tags and backplane switching circuits for displays, such as signage, readers, and liquid crystal displays, where high switching speeds and/or high density are not essential. OTFTs may be made using low-cost solution or liquid fabrication techniques. They also have attractive mechanical properties such as being physically compact, lightweight, and flexible.
Recently, there has been an increased interest in organic thin film transistors which can potentially be fabricated using solution-based patterning and deposition techniques, such as spin coating, solution casting, dip coating, stencil/screen printing, flexography, gravure, offset printing, ink jet-printing, micro-contact printing, and the like, or a combination of these processes. Such processes are generally simpler and more cost effective compared to the complex photolithographic processes used in fabricating silicon-based thin film transistor circuits for electronic devices. To enable the use of these solution-based processes in fabricating thin film transistor circuits, solution processable materials are therefore required.
In this regard, gate dielectric layers may be formed by these solution-based processes. However, the gate dielectric layer so formed should be free of pinholes and possess low surface roughness (or high surface smoothness), low leakage current, a high dielectric constant, a high breakdown voltage, adhere well to the gate electrode, be stable in solution at room temperature, and offer other functionality. It should also be compatible with semiconductor materials because the interface between the dielectric layer and the organic semiconductor layer critically affects the performance of the TFT.
Most solution processable polymers used in gate dielectric layers usually have low dielectric constants and do not contain crosslinkable functional groups, so a considerable dielectric thickness is required to reduce gate leakage current to an acceptable level. As a result, the capacitance of the dielectric layer is usually low, leading to high operating voltage and low mobility. Therefore, there is a need of solution processable polymers with high dielectric constant, crosslinkable functional groups, as well as gate dielectric layers formed by such polymers having a certain thickness, high dielectric constant, and high capacitance.